In recent years, there has been a tremendous increase in the use of contact lenses. This has, in part, coincided with the expansion of polymer and plastics technology. Various types of contact lenses have become available including hard, rigid, gas-permeable, flexible and soft hydrogel depending upon the characteristics of the materials employed to form the lens. The soft hydrogel lenses are normally formed from cross-linked hydrophilic polymers and copolymers such as 2-hydroxyethylmethacrylate, 2,3-dihydroxypropylmethacrylate, methylmethacrylate, methacrylic acid, N-vinyl-2-pyrrolidone, etc., which can be hydrated with 20-85 percent water. See Refojo, Encyclopedia of Chemical Technology, Kirk-Othmer, Vol. 6, 3rd Edition (1979), pages 720-2.
Various problems are encountered in the sterilizing or disinfecting of contact lenses. It is, of course, mandatory that sterilization or disinfection of the lenses be achieved prior to introduction of the lens into the eye. The eye is an extremely sensitive organ and certain types of microbial infection can cause damage or even blindness in a very short time. Also, in view of the sensitive nature of the eye, especially in certain individuals, it is important to avoid as much as possible contacting the eye with the agents which are effective in destroying microorganisms responsible for causing microbial infection.
Many antimicrobial agents are known which are useful to achieve sterilization or disinfection of contact lenses. Among these are chlorhexidine, thimerosal, benzalkonium chloride, Bradosol.RTM. and the like. These agents are known to provide especially good sterilizing and disinfecting properties. It is known, however, that over time these agents can become concentrated in the hydrogel soft contact lenses and may be subsequently released onto the cornea of the eye during wearing of the lenses. This can cause chemical burning of the cornea and/or an allergic response in the wearer even at low concentrations.
Fu, in U.S. Pat. No. 4,388,229, has proposed a contact lens rejuvenating solution which is said to be useful in removing occluded and adsorbed cationic and anionic agents such as bactericides, preservatives and germicides from contact lenses. In accordance with Fu, a contact lens which has a build-up of the cationic or anionic agent is subjected to treatment with the solution to remove the agent and thereby rejuvenate the lens.
Fu does not provide a sterilizing or disinfecting solution for the lens. Fu provides a solution which is useful in conjunction with and as a separate step from a sterilizing or disinfecting system. The lenses are separately subjected to sterilizing or disinfecting and then, after build-up of the chemical agent in the lenses has occurred, they are subjected to rejuvenation with the Fu solution.
A further problem with the Fu solution would appear to be one of storage stability. The formulation of Fu would have to be maintained under sterile conditions since it could not itself contain any cationic or anionic preservative agent since such agent would be taken up by the cationic and/or anionic exchange resin in the formulation. Thus, a long time storage of the Fu formulation by the user after opening would appear to be precluded.
Heyl et al., U.S. application Ser. No. 461,988, filed Jan. 8, 1990 (now U.S. Pat. No. 5,056,689), discloses methods and devices for removing preservatives from ophthalmic solutions. In accordance with Heyl et al., a dispensing device is provided which contains an ophthalmic solution containing a preservative agent such as a quaternary ammonium compound. The solution is dispensed from the container outlet which contains scavenging means for removing the preservative from the solution as it is dispensed through the outlet. Thus the solution exiting the container outlet is preservative-free. In accordance with that invention, the ophthalmic solution contacting the eye or a contact lens will not contain preservatives.